1. Field of the Invention
The present invention relates to an optical scanning apparatus which is used for a copying apparatus, a laser beam printer, or the like.
2. Description of the Related Art
Hitherto, a laser light source unit in which a semiconductor laser and a collimator lens have been constructed as a unit is assembled to an optical scanning apparatus which is used for an image forming apparatus of an electrophotographic type such as copying apparatus, laser beam printer, or the like. When the laser light source unit is assembled to a frame member of the optical scanning apparatus, it is necessary that an optical axis which has been predetermined according to a layout of the semiconductor laser and the collimator lens in the laser light source unit is precisely positioned to the frame member. For this purpose, as a construction which has often been used hitherto, there is a construction in which a laser holder 10 to hold a semiconductor laser and a collimator lens is fitted into a fitting hole H10 provided in a side wall of an optical box H and an attaching portion 18 of the laser holder 10 is fixed with screws K2 in a state where it has been abutted to the side wall of the optical box H in an optical axial direction (refer to Japanese Patent Application Laid-Open No. 2002-244062). However, in the case of such a construction, since the screws are used to fix the laser holder 10 to the optical box H, the number of parts increases. Since a space adapted to abut the attaching portion 18 of the laser holder 10 to the side wall of the optical box H and fix the attaching portion with the screws is necessary, it becomes an obstacle to miniaturization of the optical scanning apparatus. Particularly, in the case of using a plurality of laser light source units having a plurality of semiconductor lasers, since it is considered to closely arrange the plurality of laser light source units in order to use a laser circuit board in common and to simplify the assembling work, such a construction is disadvantageous in terms of the miniaturization of the optical scanning apparatus.
Therefore, as a construction to solve the latter problem, a construction in which a plurality of laser light source units are fixed by one spring without using any screws has been disclosed in Japanese Patent Application Laid-Open No. 2004-037836. FIG. 1 is a schematic diagram illustrating a plurality of laser light source units fixed with one spring in the related art.
In FIG. 1, a laser light source unit 530 has a semiconductor laser 539, a collimator lens 538, a laser holder 504, and the like. In this example, the two laser light source units 530 are provided.
Ribs 506 in a channel member cross sectional shape having an almost U-character shape (cross section in which two members are vertically extended from both edges of a horizontal member) are projected on an optical box 536 on which a polygon mirror, a scanning lens, and the like (not shown) have been attached. A plate spring 503 is provided for the optical box 536. The laser holder 504 is urged to the ribs 506 by arm portions 503a of the plate spring 503, thereby fixing the laser light source units 530 to the optical box 536.
FIG. 2 is a schematic diagram illustrating a color image forming apparatus having an optical scanning apparatus to which the laser light source units in the related art have been assembled.
According to the color image forming apparatus illustrated in FIG. 2, images of four colors of Y, M, C, and Bk are formed on surfaces of four photosensitive drums 610 and overlaid onto a transfer belt 611, thereby forming a full color image. For this purpose, an optical scanning apparatus 600 has the two laser light source units 530, thereby forming the images of two colors. In the color image forming apparatus illustrated in FIG. 2, the two optical scanning apparatuses 600 are provided, thereby coping with four colors. The optical scanning apparatus 600 has therein a polygon mirror 601, scanning lenses 602 and 603, and reflecting mirrors 604.
However, in the case of the related art as mentioned above, a force of constraint by the urging force applied by the plate spring 503 is weak. When an external stress (for example, a difference of thermal expansion of the members due to a temperature change, attachment of a laser driver circuit board (not shown), or the like) is applied, there is a risk that the position of the laser light source unit changes. If the position of the laser light source unit changes, a change in position of a scanning line on the photosensitive drum or a deterioration of image forming performance occurs.
Since the plate spring 503 is used to fix the laser light source units 530 to the optical box 536, the number of parts increases.